A number of optical identification systems have been created to encode and decode digital data based on the image capture of a visible two-dimensional mark printed on the surface of a medium, such as a paper document. Such systems and their corresponding methods generally encode data in the image of the mark, which mark is detected by optical means and decoded back into the original data. Bar codes are examples of such visible two-dimensional marking systems. However, of particular recent interest are several examples of two dimensional graphical indices used in publishing applications.
In these prior art systems, the graphical indices (also referred to as “graphical indicators” or “marks”) are made up of a plurality of individual visual elements. These visual elements are variously referred to as “picture elements,” “optical indexes,” or simply “dots.” Visual elements in prior art systems are generally defined to have uniform attributes, including size and shape. Moreover, the structure of a mark is often configured in a grid arrangement with an explicit (or implicit) and fixed Cartesian axis, or in an isotropic arrangement with express arrangements and relative position of visual elements within the individual marks. Data is encoded in the mark by the presence, absence or relative positions of individual visual elements within the individual mark's grid or isotropic arrangement. Thus a single encoded mark appears visually as a pattern of dots.
For example, U.S. Pat. No. 7,328,845 (referred to as the '845 patent), discloses a system where each graphical index includes a plurality of state zones. Each of the state zones may be blank or may include a micro-unit (such as a dot), where a blank state zone represents a binary “0” and a state zone having a micro-unit represents a binary “1” value. In the '845 Patent, each individual graphical index represents an indicator information, and the indicator information corresponds to an additional information. In the '845 patent, the indicator information is determined by the binary value graphically represented by the micro-units in the graphical index. Example embodiments of graphical indices as taught by the '845 patent are shown in FIGS. 1a and 1b. As also shown in FIGS. 1a and 1b, each of the graphical indices in a given area includes an identical header (111) intended to provide orientation information so that the optical reader can decode the graphical index irrespective of the orientation of the optical reader, vis-à-vis the encoded surface. In another example, FIG. 1c illustrates an isotropic graphical index as disclosed in U.S. Pat. No. 7,350,718 (referred to as the '718 patent). Similar to the '845 patent, values associated with the isotropic graphical indices in the '718 patent are determined by the binary values graphically represented by the micro-units in the index.
The existing systems have little flexibility, and convey in a single mark only a fixed and relatively small amount of data, or “payload” information. The “payload” information is typically expressed as the number of digital bits that can be obtained by decoding a single mark, and current known systems convey a payload of only 16 to 62 bits. The payload capacity of existing marking systems is fixed and not inherently variable or scalable to suit a particular application. Further, codes using many prior art systems are generally easily decoded by third parties, and thus provide little to no security for the encoded data.
The invention seeks to advance the art by addressing these and other drawbacks of the prior art. In particular, the invention seeks to provide a coding architecture having greater flexibility over a wide range of applications, and with the ability to encode larger amounts of data than previously provided for with existing systems. The inventor further seeks to provide a coding architecture for encoding and decoding digital data embedded in or on the surface of a medium with means of encrypting the encoded data to minimize the potential for unwanted decoding by users or third parties.